<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
  </head>
  <body>
    <script>
      var num = prompt('请输入数字');
      if (num < 10) {
        var result = '小于10';
      } else {
        var result = '大于或等于10';
      }
      alert(result);
    </script>
  </body>
</html>